Various human-machine interaction areas such as telerobotics, virtual reality and scientific data visualization are all emerging as important new technologies, an important feature of which is the interactive human-machine interface. A key component of the human-machine interface in these applications is the control device or controller which allows users to manipulate 3 dimensional objects, real or virtual. These control devices are referred to as 6 degree-of-freedom (DOF) controllers because they have three translational degrees of freedom and three rotational degrees of freedom. In computer applications the control device is normally referred to as an input controller. The 6 DOF controller allows a user to manipulate 3 dimensional real or virtual objects under computer control. Typical commercial computer input devices such as the computer mouse and track ball have two degrees of freedom.
One major class of 6 DOF input devices comprises freely moving devices. This class can be further subdivided into uncoupled unsupported devices, where the user must hold his hand in the air to use it, and mechanically coupled devices, which are potentially partially supportable. Freely moving unsupported 6 DOF input devices are usually isotonic, comprising those for which the user encounters no resistive countering forces while holding and moving the device. These include the Ascension Bird.TM., the Logitech.TM. 6 D Mouse, the Flying Mouse.TM. and the Polhemus.TM.. In all such devices the user holds a control handle (or wears a glove) and moves his/her hand without support. These devices usually utilize position control mapping (pure gain control) in which the user's hand motion is sensed and proportionally mapped to the position and orientation of a selected 3D object on a computer screen.
A major drawback to current unsupported isotonic position devices is their comparatively large operating volume and resultant fatiguing which arises from a user moving his/her arm about unsupported. An additional inherent limitation of these isotonic position control devices relates to the restricted operational range of translational motion due to limited arm extension length and limited rotational movement due to limited rotational range of the arm and hand. In the case of glove type unsupported isotonic 6 DOF input devices this limitation can be overcome by a system of "clutching", wherein the user clutches or declutches, in order to enable the control mechanism by means of a switching device which is activated by the hand's opening or closing. Typically, while the hand is opened the object being manipulated remains fixed and while closed it responds to the hand's movement. This procedure is completely analogous to the lifting up of a conventional 2 DOF computer mouse and replacing it elsewhere on the control surface. In the 6 DOF case, the position of the user's hand is sensed relative to a starting position, defined by the point at which the hand starts to close and activates a switch, and the distance travelled is determined and mapped onto the 3D object being controlled. In contrast to the 2 DOF case, this is not a completely satisfactory solution since it involves a set of extra hand motions, it takes up more time, and it requires potentially awkward and fatiguing translational and rotational movements of the user's unsupported limb. Designers of such systems therefore strive to minimize the frequency and extent of these control movements, primarily by means of gain control. Unfortunately, reducing this factor excessively can result in a control gain which is too high and thus too sensitive to the user's input movements.
Another class of freely moving input control devices comprises those which are somehow mechanically coupled to an external frame, rather than being unsupported. One such device is the Spidar (Masahiro Ishii and Makoto Sato, "A 3D Interface Device With Force Feedback: A Virtual Work Space For Pick-And-Place Tasks", in Proceedings of IEEE Virtual Reality Annual International Symposium" Sep. 18-22, 1993, Seattle, Wash. USA), comprising a finger harness mounted within a lattice of wires whose displacements collectively permit the sensing of 6 DOF translations and rotations, while providing force feedback through the mechanical coupling means. Another is the Immersion Probe.TM. (produced by Immersion Human Interface Corporation, P.O., Box 8669, Palo Alto, Calif.) comprising a stylus mounted on the end of a series of mechanical linkages. Both devices work typically in the position control mode wherein the manipulated 3D object moves in proportion to the movement of the finger harness or stylus. Due to the presence of mechanical coupling, both kinds of device have a restricted range of motion. Furthermore, even though the mechanical linkages in these devices are in principle able to provide some kind of support to the user's hand, fatiguing can still occur due to the need to move the whole hand to effect control movements.
Another major class of 6 DOF input devices are substantially isometric devices, which do not move but are sensitive to the translational and rotational forces imparted by the user. Known isometric 6 DOF controllers include the Spaceball.TM. (U.S. Pat. No. 4,811,608) and the Space Control Mouse (made by DFL in Germany and sold by Logitech Corporation). Isometric devices are generally used in the rate control mode so that the forces and torques applied to a control handle are converted to a velocity of the virtual or real 3D object being controlled. A major drawback to this type of controller is that the user's hand operates in a substantially stationary posture which limits the amount of somatosensory feedback experienced by the user.
Neurophysiological studies have shown that various parts of the human body are anatomically reflected in the brain disproportionately relative to their physical size and mass. Of particular interest to the inventors is the fact that representations of the fingers and the hands in both the somatosensory cortex and the motor cortex are much richer than those of the wrists, elbows and shoulders. The inventors therefore contemplate performance enhancement if fine muscle groups (i.e. fingers) are allowed to take part in handling an input device.
The inventors have studied how human performance in 6 DOF tasks vary according to the muscle groups employed. The implications of this research are that if performance for a given task is higher when a particular muscle group is employed, then input devices can be designed according to the use of that muscle group. The human upper limb as a whole (from shoulder to finger tips) has evolved to be highly dextrous and yet powerful. Every part of the upper limb has a purpose and function. The larger muscle groups that operate the wrist, elbow, and shoulder have more power and a larger range of movement than the fingers. However, the smaller muscle groups that operate the fingers and thumb have more dexterity. When all the parts work in synergy, movement range and dexterity can both be maximized. The invention disclosed here relates primarily to freely moving devices which exploit movement of all of these muscle groups.
The results of the present inventors' studies show that performance improvement in 6 DOF fine manipulation input tasks does not necessarily lie simply in moving operations from the large muscle groups to the smaller ones, but rather in using the small muscle groups in addition to the large ones. This can be achieved by permitting the user to rotate the manipulandum freely with his/her fingers. An important advantage of adding the ability to freely rotate the manipulandum with the fingers greatly reduces the frequency of situations in which the user's hand finds itself in an anatomically singular orientation. This also has the important distinct advantage of decreasing the frequency required for clutching and declutching operations.
The majority of existing designs of freely moving 6 DOF devices, such as the "Bat" (Ware, C. "Using Hand Position For Virtual Object Placement". The Visual Computer, 6, (1990), 245-253); the "Cricket" (Digital Image Design Inc. The Cricket, product information. New York, N.Y., 1993); and the 3D mouse are similar to the glove design in assigning wrist, elbow and shoulder muscles for manipulating the six degrees of freedom; however, none of these devices makes use of the fingers for 6 DOF manipulation.
The role of some kind of a button or other switching mechanism on the input device is essential for enabling communication of discrete information to the control computer. Some hand-held input devices are available having a discrete localized button, or buttons, located on the housing. A typical example of such a device is disclosed in U.S. Pat. No. 5,363,120 issued to Drumm and includes a hand held computer input device for controlling cursor movement on a display screen and is provided with several switches mounted in the housing. The limitation of this type of device is its fixed button location(s) so that users cannot freely roll the device between their fingers and thus make use of the superior dexterity of their fingers.
What is needed in input device which makes use of all parts of the associated limb, according to their respective advantages. Accordingly, it would be advantageous to provide a 6-DOF control device which more fully utilizes all the available muscle groups of the upper limb, as well the thumb and fingers, but which permits the user to communicate discrete button-pressing type information to the computer regardless of the position of the device within the user's fingers.